Laser imaging systems are known in the art for analyzing laser beams and for observing a laser interaction area in material processing.
Ghost images at an image plane in a laser imaging system, such as on a pixelated detector of a Charged Coupled Device (CCD) or Complementary Metal-Oxide-Semiconductor (CMOS) digital camera, or other digital imaging system, are caused by reflections of light from the optical media of the imaging system, wherein the optical media have non-zero reflection and transmission coefficients. The non-zero reflection and transmission of light is a result of the difference in the refractive index on either side of the interface. At the interface, a portion of the incident light from a laser beam is transmitted at the surface of the optical media, while another portion of the incident light is reflected. The reflected light then propagates back to another optical media surface, which is reflected again and eventually propagates to the image plane, resulting in the pixelated detector sensing a ghost image. The ghost image is undesirable because it negatively affects the ability of the pixelated detector to accurately measure the laser beam or distort an image.
While anti-reflection coatings for the optical media are known in the art for reducing the ghost images, the known anti-reflection coatings are not effective in mitigating the ghost reflections in applications utilizing pixelated detectors that are extremely sensitive to the ghost images or when the wavelength band is broader then about 25 nm to 50 nm.
Accordingly, there is a need in the art for an apparatus and method for reducing the ghost images seen by a detector of a laser imaging system.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how the limitations of the art could be overcome.